Device for monitoring the alleyways between shelf units in a warehouse

ABSTRACT

The alleyway-monitoring device disclosed has, mounted at different heights, two light barriers (16 to 26, 28 to 30), the higher of which is at a height at which the light beam can be broken only by fork-lift trucks. The light barriers produce output signals which enable the direction of motion of the objects which break the beam to be determined, the output signals being passed to associated up/down counters (50, 52) which are in turn connected to the inputs of a monitoring circuit (54). The monitoring circuit triggers an acoustic alarm (56) if non-permitted counter-reading combinations occur.

FIELD OF THE INVENTION

The invention concerns an alleyway monitoring device.

BACKGROUND ART

In warehouses with high shelf units special fork-lift trucks have to beused to reach the higher shelves and to move heavier objects. It iseasier to place smaller items onto and remove them from the shelves byhand. As the driver of a fork-lift truck often does not have an adequateview of the alleyway from behind the lift and the load there is thedanger of collision between the fork-lift truck and persons doing manualorder-picking work.

To avoid such accidents it has already been proposed to provide abarrier at the end of each alleyway which, in conjunction with a lightbarrier and associated electronics, guarantees that only one person orone truck can be in the alleyway at any time. Such barriers greatlyimpede work, however, because even when the alleyway is empty itsopening must be awaited. This is why the personnel often disconnect suchbarriers so that they can work more quickly. Furthermore, with theseknown monitoring devices, access to the alleyway is not possible if aperson doing manual order-picking work is in the alleyway and a secondperson, also working manually, wishes to enter the alleyway.

The risk of accidents in alleyways between shelf units could also beremedied in another way by, for example, providing for each fork-lifttruck a monitoring device operating on the basis of ultrasound whichmonitors the space immediately in front of the truck for foreignobjects. This possibility does, however, have the disadvantage that manyfalse alarms are generated by other obstacles adjacent to the alleyway.The equipping of the various fork-lift trucks with a monitoring deviceof this kind also involves high costs.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a monitoring devicefor an alleyway between shelf units which does not normally impedeaccess to an alleyway but triggers an alarm if a non-permittedcombination of fork-lift trucks and/or persons is present in thealleyway.

In the monitoring device according to the invention the distinctionbetween persons and fork-lift trucks is made by two light barriers whichare mounted at different heights. An upper light barrier operates atsuch a height that it can only be broken by the high fork-lift trucks. Alower light barrier is mounted at such a height that it can also bebroken by persons walking in the alleyway. Both light barriers are sodesigned that they report not only the fact that they have been brokenbut also the direction of motion of the object breaking them. This can,for example, be achieved by means of two light barriers spaced apart inthe longitudinal direction of the alleyway, whose output signals areevaluated via a suitable signal connection circuit. The output signalsof the light barriers processed in this way can then be transmitteddirect to an up/down counter whose counter reading directly correspondsto the number of fork-lift trucks in the alleyway and/or the number ofobjects in the alleyway (=trucks plus persons). A monitoring circuitsupplied with the counter readings then generates, according to apre-set table supplied to it, an alarm signal whenever a non-permittedcombination "number of fork-lift trucks to number of objects" isdetermined.

The monitoring device according to the invention can also be installedin existing alleyways between shelf units with little technical outlay.Barriers and other obstacles which impede work are not required. Work inthe alleyway is completely unimpeded until an alarm is triggered. Inthis case, which is not very frequent in practise, the driver of thefork-lift truck must then stop his truck until the alarm has beencancelled by an authorized person after the situation has been verified.

Advantageous further embodiments of the invention are disclosed asfollows.

In a monitoring device using two light beams in wide alleyways it isalso possible separately to detect two persons entering or leaving analleyway alongside each other.

A monitoring device a lower light barrier and a third light barriermakes it possible to differentiate between persons walking behind eachother and persons carrying an object in front of them.

The embodiment of the invention using a fourth light barrier alsopermits differentiation between a person and an order-picking trolleybeing pushed by a person.

With the embodiment of the invention using an acoustic alarm acompulsory immobilization of the fork-lift trucks is obtained whenhazard situations are detected.

With a monitoring device using display devices the fork-lift trucks andpersons moving about in the shelf unit have a constant view of thosealleyways for which there is currently potential access and thosealleyways which are temporarily blocked for safety reasons.

The embodiment of the invention using calculated and displayed schedulesmakes it possible for the fork-lift trucks and persons carrying outorder-picking work to be guided in the performance of the order-pickingwork assigned to them in such a way that there are only short waitingtimes at the alleyways that are blocked for safety reasons.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below with the aid of embodiments andthe accompanying drawings, where:

FIG. 1 shows a front view of two rows of a warehouse with high shelfunits together with a block diagram of a monitoring device for alleywaysbetween shelf units;

FIGS. 2 to 5 show modified geometries for the light barriers of themonitoring device for alleyways between shelf units according to FIG. 1;and

FIG. 6 shows a block diagram of a control center of a warehouse withhigh shelf units together with a fork-lift truck.

FIG. 7 is a flow chart detailing the function of the up/down counters 50and 52 and determination of a non-permitted situation by the computer100.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, 10 and 12 show two rows of shelves in a warehouse with highshelf units, which have open shelves to the right and the left and analleyway 14 in between.

A transmitter unit 16 which generates a light beam 18 is provided in theupper left-hand area of the shelf row 12. This light beam is picked upby a receiver unit 20 opposite, which is mounted in the upper right-handsection of the shelf row 10.

Lying behind the transmitter unit 16, and displaced slightly downwardsfor improved representation, a further transmitter unit 22 whichgenerates a light beam 24 is provided. This impacts on a receiver unit26 which is provided on the shelf row 10.

In the lower area of the alleyway 14 two further light barriers aresimilarly provided, which comprise a transmitter unit 28, a light beam30, a receiver unit 32 as well as a transmitter unit 34, a light beam 36and a receiver unit 38, the arrangement being similar to that of the twoupper light barriers but with the sole difference that the light beams30, 36 travel approximately at a height of 80 cm whereas the light beams18, 24 travel at a height of approximately 2.20 m.

The transmitter units 16, 22, 28, 34 are connected via a line 40 to afeeder bar 42 which is supplied with pulsed direct current oralternating current from an exciting circuit 44, as is customary inlight barriers for the electronic suppression of extraneous light.

The receiver units 20, 26 are connected to the inputs of a signalprocessing circuit 46, the outputs of the receiver units 32 and 38correspondingly to the inputs of a signal processing circuit 48. Roughlyspeaking the two signal processing circuits 46, 48 operate in such a waythat they determine from the time sequence of the breaking of the lightbeams whether the object breaking the light beams 18, 24 or the lightbeams 30, 36 is moving into or out of the alleyway. As appropriate thesignal processing circuits 46, 48 provide at their one output adirectional signal which is transmitted to the "+/-" control terminal ofan associated up/down counter 50 or 52, the counter terminal "C" ofwhich receives a counting pulse whenever the corresponding pair of lightbeams is broken.

In this way the reading on the up/down counter 50 corresponds to thenumber of fork-lift trucks in the alleyway. The reading of the up/downcounter 52 corresponds to the total number of moving objects in thealleyway (fork-lift trucks plus persons).

A monitoring circuit 54 which evaluates the two counter readings isconnected to the outputs of the up/down counters. By deducting thereading of the up/down counter 50 from the reading of the up/downcounter 52 the monitoring circuit 54 determines the number of persons inthe alleyway who break only the lower light beams 30, 34 when enteringand leaving the alleyway.

By means of appropriate programming a table which gives all thecombinations of the readings of the up/down counters which areunacceptable for safety reasons is filed in the monitoring circuit 54.When a non-permitted counter reading combination of this kind isencountered the monitoring circuit 54 produces a signal at its output,via which an acoustic alarm 56 is switched on permanently. The alarm canonly be switched off by operating a re-set switch 58 which is connectedto the alarm interception circuit of the monitoring circuit 54 and canonly be operated by an authorized person and is designed as a keyswitch, for example, for this purpose.

The entire monitoring circuit associated with the alleyway 14 isdesignated as 60 in FIG. 1. A similar monitoring circuit 60' is providedfor the adjacent alleyway 14', which is similarly equipped with lightbarriers, as described above for the alleyway 14 (reference numbers witha coma).

The output signals of the different monitoring circuits 60, 60' etc. arecombined by an OR circuit 62 which triggers an additional alarm 64mounted in a central control room of the warehouse (the alarm 56 isspatially mounted in the alleyway 14).

In the modified monitoring device according to FIG. 2 the lower lightbeams 30, 36 travel in a vertical plane inclined at an angle parallel toeach other. In the embodiment as shown in FIG. 3 the light beams 30 and36 are inclined in opposite directions and intersect in the center ofthe alleyway.

In the embodiment according to FIG. 4 the light beams 30 and 36 are bothinclined in a direction perpendicular to the plane of the drawing. Thetwo light beams 30, 36 are therefore broken at exactly the same time bytwo persons entering the alleyway next to one another or two personsleaving the alleyway next to each other at the same time, and themonitoring circuit 54 can distinguish this situation from the successivebreaking of the light beams 30, 36 as caused by a single person.

In the embodiment according to FIG. 5 the lower light beams 30, 36 aremoved immediately adjacent to the floor of the alleyway, are 5 cm abovethe floor, for example. Additionally a center light barrier is providedat a height of approximately 80 cm which comprises the transmitter unit66, the light beam 68 generated by this, the associated receiver unit 70and the transmitting unit 72, the light beam 74 generated by this andthe associated receiver unit 76.

A fourth light barrier is provided at a height of approx. 1.55 m andsimilarly comprises a transmitter unit 78, the light beam 80 generatedby this, the associated receiver unit 82 and a transmitter unit 84, thelight beam 86 generated by this and an associated receiver unit 88. Thelight beams 80, 86 again have a component travelling perpendicular tothe plane of the drawing, so that they intersect in plan view, so that aclear resolution of persons walking next to one another is obtained inthe neck or head area (depending on the height of the persons).

The additional light barriers are again connected to associated signalprocessing circuits and associated up/down counters. The outputs ofthese up/down counters are additionally connected to the monitoringcircuit 54. This can therefore undertake an even finer resolution of theheight of the passing objects and therefore additionally distinguishbetween a person and objects carried by a person and/or an order-pickingtrolley pushed by a person.

In the embodiments described above, for the purposes of the descriptionand for reasons of simplicity it was assumed that the alleyway 14 issealed off at the rear end by a wall or similar. If the alleyway canalso be entered or left at the rear end or at a place at the side,similar light barriers are provided there, as in the end shown inFIG. 1. Signal processing circuits like the signal processing circuitsdesignated as 46 and 48 in FIG. 1 are then associated with these lightbarriers. The output signals of the signal processing circuitsassociated with the further rear and/or lateral light barriers caneither be transmitted to separate up/down counters associated with themwhich are then also connected to the monitoring circuit 54 which thendetermines the number of objects, persons and fork-lift trucks bycomparing the various counter readings. Alternatively the outputs of thelight barriers at the same height for the front and rear alleyway endand lateral accesses can be combined via an OR circuit and transmittedto a single up/down counter associated with this monitoring height.

The output signals of the up/down counters 50, 52 for the differentalleyways can also be used to indicate in advance to the fork-lifttrucks and the persons moving about in the warehouse which alleywaysthey can enter and which are currently blocked for safety reasons.

For this purpose the output signals of the up/down counters 50, 52 of analleyway under consideration are additionally transmitted to adders 90,92. The second input of the adder 92 permanently receives a signal whichcorresponds to the digital representation of the number "1". The secondinput of the adder 90 is supplied with the signal "1" via a controllableswitch 94. When the switch 94 is closed, numbers which would correspondto the reading of the up/down counters 50, 52 if a further fork-lifttruck had moved into the alleyway under consideration are obtained atthe outputs of the adders 90, 92. If the switch 94 is open, the numbersobtained at the outputs of the adders 90, 92 correspond to a readingwhich would be obtained if a further person had moved into the alleywayunder consideration. The output signals of the adders 90, 92 aretransmitted to a monitoring circuit 96 which is similarly constructed tothe monitoring circuit 54 and supplies an alarm signal at its output ifan alarm condition were to be obtained because of the additional entryof a fork-lift truck (switch 94 closed) or additional entry of a personinto the alleyway (switch 94 open).

The monitoring circuit formed by the adders 90, 92 and the monitoringcircuit 96 is designated as a whole by 98. Like the output signals offurther monitoring circuits 98' and 98" for further alleyways, itsoutput signal is transmitted to inputs of a control computer 100. Thisoperates in conjunction with an in/output unit 102 into which thevarious order-picking tasks are inputted as well as the fork-lift trucksand persons to be employed for these tasks.

Periodically the control computer 100 evaluates the accessible andblocked alleyways for the various fork-lift trucks and persons, opening(person) or closing (fork-lift truck) the switch 94 depending on theobject to be simulated.

For the fork-lift trucks and order-picking persons the control computer100 has an associated modem 104 on the output side which cooperates witha modem 106 set to the same frequency, which the order-picking personcarries with him or which is mounted on the corresponding fork-lifttruck. Such a truck is illustrated diagrammatically as 108 in FIG. 6.

The modem 106 is connected to a display unit 110. Via the modems 104 and106 the control computer 100 continuously represents on the display unit110 which alleyways are currently blocked for safety reasons and whichare accessible.

Taking into account the currently freely accessible alleyways, theorder-picking work to be carried out and the instructions already passedto other fork-lift trucks and persons the control computer 100 can alsocompile a schedule for an order-picking person or a fork-lift truckproviding no or only short waiting times at blocked alleyways.

As FIG. 6 shows, the fork-lift truck 108 also carries a microphone 112which via an amplifier 114 can open a controllable and usually closedemergency stop switch 116 which is connected in series with the normalkey switch 118 of the truck.

FIG. 7 is a flow chart detailing the functions of the up/down counters50 and 52, the determination of a non-permitted combination to triggerthe alarm 56 and the transfer of information from the control computer100 to the display device 110. As is evident from FIG. 7, the up/downcounters 52 and 50 track the objects and vehicles in the alleyway. Withthis information, the number of persons in the alleyway can becalculated by subtracting the number of sensed vehicles from the numberof sensed objects.

Then, the number of persons and number of vehicles in an alleyway iscompared to a non-permitted combination in a table which givescombinations of the number of persons and number of vehicles in analleyway which would be unacceptable for safety reasons. For example, ifa fork-lift truck entered an alleyway, the computer 100 can compare thenumber of persons and number of vehicles for each alleyway to determinewhich alleyways are blocked or have a non-permitted combination ofpersons and vehicles. Based on this evaluation, the computer can compilea schedule for the display device 110 associated with a fork-lift truckor person so that the fork-lift truck or person only has to wait a shorttime at alleyways that may be blocked.

I claim:
 1. A monitoring device for an alleyway defined by a pair ofupstanding structures, the alleyway having at least one accessible end,comprising:at least two light barrier assemblies (16 to 26, 28 to 38)mounted at a first height level and a second height level, respectively,on said pair of upstanding structures at said at least one accessibleend, each of said light barrier assemblies supplying an output signalresponsive to an object breaking light beams formed by said lightbarrier assembly, the output signal being based on the particularsequence of breaking of the light beams of said light barrier assembly,the sequence being based on a direction of motion of the object whichbreaks the light beams; an up/down counter (50, 52) for each of saidlight barrier assemblies, each up/down counter being supplied with theoutput signals of its associated one of said light barrier assemblies(16 to 26, 28 to 38); and a monitoring circuit (54) being connected tooutput signals of the up/down counters (50, 52), said monitoring circuit(54) supplying an alarm signal whenever said monitoring circuit (54)determines a pre-set combination of readings of said up/down counters(50, 52).
 2. Monitoring device as claimed in claim 1, wherein at leastone of said at least two light barrier assemblies (28 to 38) has twolight beams (30, 36) inclined with respect to the vertical in a verticalplane.
 3. Monitoring device as claimed in claim 1, wherein at least oneof said at least two light barrier assemblies (28 to 38) has two lightbeams (30, 36) inclined in opposite directions with respect to vertical.4. Monitoring device as claimed in claim 1, wherein at least one of saidat least two light barrier assemblies (28 to 38) has two parallel lightbeams (30, 36) each being inclined with respect to horizontal andintersecting along a longitudinal center plane of the alleyway (14). 5.Monitoring device as claimed in claim 1, wherein said first height levelis immediately adjacent to a floor of the alleyway (14), and a thirdlight barrier assembly (66 to 76) is provided at a third height levelbetween said first and second height levels.
 6. Monitoring device asclaimed in claim 5, further comprising a fourth light barrier assembly(78 to 80) being provided at a height that is between the second heightlevel and the third height level.
 7. Monitoring device as claimed inclaim 1, wherein an acoustic alarm (56) generates said alarm signal,said acoustic alarm being triggered by the monitoring circuit (54). 8.Monitoring device as claimed in claim 1, further comprising a re-setswitch (58) associated with the monitoring circuit (54), said re-setswitch operable to interrupt said alarm signal.
 9. Monitoring device asclaimed in claim 1, wherein a plurality of monitoring devices (60, 60')are used with a plurality of alleyways, and a single central alarm (64)is triggered by any one of said monitoring circuits of said plurality ofmonitoring devices (60, 60').
 10. Monitoring device as claimed in claim7, wherein fork-lift trucks are provided with a microphone responding tothe signals of the acoustic alarm (56), the microphone used to switchoff all movement functions of the fork-lift truck upon receiving thesignals from the acoustic alarm.